From: Maria Matejka <mq@ucw.cz>
Date: Fri, 17 May 2024 21:21:38 +0000 (+0200)
Subject: Loop run waits until pingers finish
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=48d090aacc76e6f9f9d2f18b7fa728565c6785c8;p=thirdparty%2Fbird.git

Loop run waits until pingers finish

This ensures that if somebody passes an event to a loop which
has just started executing, then the event gets picked up. Otherwise
there is a race condition causing stray events pending in queue
but without the ping (because the run actually finishes too fast
to pickup the later events).
---

diff --git a/sysdep/unix/io-loop.c b/sysdep/unix/io-loop.c
index be79946c6..f777d210e 100644
--- a/sysdep/unix/io-loop.c
+++ b/sysdep/unix/io-loop.c
@@ -1449,6 +1449,17 @@ birdloop_run(void *_loop)
   account_to(&loop->locking);
   birdloop_enter(loop);
   this_birdloop = loop;
+
+  /* Wait until pingers end to wait for all events to actually arrive */
+  for (u32 ltt;
+      ltt = atomic_load_explicit(&loop->thread_transition, memory_order_acquire);
+      )
+  {
+    ASSERT_DIE(ltt == LTT_PING);
+    birdloop_yield();
+  }
+
+  /* Now we can actually do some work */
   u64 dif = account_to(&loop->working);
 
   if (dif > this_thread->max_loop_time_ns)